3 Basics

LXM32M

 

 

3.4Modbus services - "Function Code"

The table below provides an overview of the available Modbus serv- ices:

"Function

Meaning under Modbus

Meaning from device per-

Code"

 

spective

 

 

 

3

Read Multiple Registers

Reading a parameter

 

 

 

8

Diagnostics

Diagnostics

 

 

 

16

Write Multiple Registers

Writing a parameter

 

 

 

23

Read/Write Multiple Registers

Reading and writing parame-

 

 

ters

 

 

 

43

Read Device Identification

Subcode14

 

 

 

 

 

90

UMAS File Transfer (Upload)

 

 

 

3.4.1"Function Code" 3 (Read Multiple Registers)

This "Function Code" 3 (Read Multiple Registers) allows you to read several consecutive parameters, starting at any address.

Modbus request Structure of the Modbus request:

Field

Bytes

Value

Meaning

 

 

 

 

Function Code

1

3 = 03h

Read Multiple Registers

 

 

 

 

Starting Address

2

(various)

Address of the first parameter to be read

 

 

 

 

Quantity Of Regis-

2

2 * n

Number of 16 bit values to be read

ters

 

 

(1 parameter has the value 2 since a parameter

 

 

 

consists of a 32 bit value)

 

 

 

 

Modbus response Structure of the positive Modbus response:

Field

Bytes

Value

Meaning

 

 

 

 

 

Function Code

1

3

= 03h

Read Multiple Registers

 

 

 

 

 

Byte Count

1

4

* n

Number of data bytes

 

 

 

 

Registers Value

4 * n

(various)

Parameter values

 

 

 

 

 

Structure of the negative Modbus response

Field

Bytes

Value

Meaning

 

 

 

 

Function Code

1

03h + 80h = 83h

Read Multiple Registers

 

 

 

 

Exception Code

1

01h ... 04h

See chapter

 

 

 

"3.3.2 Modbus response to a Modbus request"

 

 

 

 

0198441113843, V1.01, 01.2012

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Modbus-TCP module

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Schneider Electric LXM32M manual Modbus services Function Code, Function Code 3 Read Multiple Registers